1. Field of the Invention
The invention relates to a laser diode module with a built-in high-frequency modulation IC (abbr. for integrated circuit), and more particularly to a laser diode module that is used to remove the reflected noise generated as the laser beam reads the signal to be played back and that is directly packaged within a metal cap.
2. Description of the Related Art
Among the important components inside a CD-ROM and DVD, the optical reader, or so called optical pickup apparatus, which reads the signals stored on the CD, is made up of several optical components, including the laser diode (LD), objective lens, hologram, and photo diode (PD).
When the laser diode acts as the optical pickup apparatus, then the problem of the reflected noise will occur. When an optical beam from the laser diode is released onto the diskette, some of the reflected light from the diskette's surface will go back to the LD, creating the fuzzy signal phenomenon. Since the laser diode vibrates on a single mode, therefore, when there is light reflected back, it will produce mode hopping, and since the output of optical volume will have massive changes, hence it will produce the reflected noise.
Therefore, in the prior technology, in order to reduce the reflected noise, a high-frequency electric current is used to produce electric circuit. Meanwhile, multimodes are used to make LDs vibrate so that even though it will create mode hopping, it will not alter the output of optical volume. It is already known that 200 MHz and above frequencies will overlap with frequencies of 20˜30 mA and above as well as the LD's electric current control, which is set as the driving current. Multimodes are used to vibrate the laser diode to reduce the reflected noise. These patents have already been applied by TOSHIBA, patent number 89111889, applied in Taiwan on Jun. 16, 2000. Patents in Japan, number 11-297014, applied on Oct. 19, 1999, and number 9-49431, applied on Mar. 4, 1997, and the U.S. Pat. No. 6,489,600, can be found.
However, in the prior technology (see FIG. 1), the laser diode chip is first placed onto the heat sink (11). In order to prevent the exposed chip from being damaged, a metal cap (12) must be sealed on top of it and dry gas with very low dew point pumped inside. The diameter of the final laser diode module (10) sealed packaging is 5.6 mm while the legs of several terminals (13) extend from the bottom of the heat sink (11). The electric circuit produced by the high-frequency electric current (21) is linked to the sealed laser diode modules (10) through a printed circuit board (PCB) (20). However, this type of structure still has the following drawbacks in the manufacturing and usage of optical pickup apparatus:    1. When manufacturing the optical pickup apparatus, a circuit board (20) for producing the high-frequency electric current must be externally attached. This not only increases the inconvenience during manufacturing, but also relies on manual adjustment of the optical output, which in turn affects production efficiency and increases manufacturing costs as well.    2. By externally attaching the circuit board (20) for producing high-frequency electric current onto the laser diode modules (10), the size of the entire device cannot become any smaller. This makes it difficult to design CD devices that demand small size and lightweight, hence it cannot be applied to some special products that require smaller sizes.    3. In addition, when the externally attached circuit (21) for producing high-frequency electric current is activated, it will result in a great deal of electromagnetic interference (EMI).